The study found that across the country charter schools -- publicly funded but privately run campuses -- have made "slow and steady progress" compared to four years ago when CREDO (Center for Research on Education Outcomes) did another study.

Nationally, the average charter school student gains in an academic year eight more days of learning in reading compared to traditional school students and makes the same learning gains in math, the new, far-reaching study found. The group's 2009 study found the average charter school student lost out in both reading and math.

Since then these schools have improved, and some poor performing charters have closed. Black students, students living in poverty and students learning English -- all groups that typically struggle in school -- have made the most notable gains in charter schools. Those students in charters, on average, outpace counterparts in traditional schools.

But the study noted that charter school students have "markedly different learning gains" across the 27 states included in the study, even with demographic differences were taken into account.

The study noted, however, that differences in states' overall academic achievement would influence whether the differences in days of learning made an actual difference to particular children.

In 11 states, such as Louisiana and Tennessee, charter students gained more in both reading and math than counterparts in traditional schools. But Florida was not among those, with its charter students lagging in reading and doing no better in math.

Still, the Florida Department of Education found good news in the report.

The report “demonstrates that the charter school sector, both nationally and in Florida, continues to improve," said Mike Kooi, executive director of the education department's office of independent education and parental choice, in a statement.

"The report highlights the fact that, similar to our traditional public school system, there are charter schools that are performing at exceptional levels," he wrote. "Charter schools that are not meeting the needs of their students should be closed. As a state, we must continue to focus on ensuring that all of our public schools are preparing students for success in college and/or career.”